The present invention relates to an extremely low energy optical processor and a method of optical processing. More particularly the processor of the present invention comprises an optical cavity defined by an optical gain medium excitable to population inversion, first and second means for imposing spatial patterns on wavefronts generated by the gain medium, and reflective means for reflecting light back to the gain medium to induce stimulated emission therein when the spatial patterns imposed by each of the first and second means have dual spatial patterns.
The present invention also relates to an active optical sensor and a method of optical sensing or pattern recognition wherein an optical cavity is defined by a gain medium, an object under investigation, a spatial light modulator, and a reflective means for reflecting light back to the gain medium to induce stimulated emission therein when spatial patterns imposed by the object and the spatial light modulator have duality.
Prior art optical computers have utilized coherent light provided from laser light sources which are external to the computation system. The externally-provided light is used for making the desired computations. Light from the external source is fed into the system and thereafter the computations are performed. Well known optical computing devices such as coherent optical correlators are examples of such prior art systems. Diffraction of laser light is exploited to compute Fourier transforms, correlations, convolutions, and to perform general transformations through the interconnections provided by the externally-generated light.
Where the laser source is external, it is held or pulsed at substantially full lasing power and the "lasing" photons are sent to the full computation path. Power requirements for operating such prior art systems thus depend upon the total computation power requirements and "laser beam waves". Power requirements are heavily dependent upon the size of the system. For example, power requirements for prior art laser-based, active sensors are larger because gain is provided external to the elements accomplishing detection and computation. In such prior art laser active sensors, full laser power is generated for illuminating the object under observation. Special detection by heterodyning and subsequent post processing are state of the art for known active sensors.
Intra-cavity modulation has been used in mode-locked and Q-pulsed laser systems. Such devices have been employed in for example, communications, radar systems, weaponry systems and other applications. For example, U.S. Pat. No. 4,658,146 relates to a laser apparatus with an extended cavity in which an information bearing medium intercepts a standing wave generated within the laser cavity. The system of U.S. Pat. No. 4,658,146 is described as switching in and out of lasing mode operation as the surface of the information bearing medium is moved to bring changing magnetic domains. As such, information encoded as the timing between domain changes can be recovered by monitoring laser operation or nonoperation.
U.S. Pat. No. 3,657,510 relates to a Q-switched laser for vaporizing or otherwise altering the surface of a target object according to a given pattern. In this regard, U.S. Pat. No. 3,657,510 discloses a laser cavity which is defined between a full mirror and a partial mirror, and which includes a laser medium, a Q-switch, and a mask. A laser medium is pumped into stimulated emission. According to U.S. Pat. No. 3,57,510, the stimulated emission occurs only at cross-sectional portions of the laser material that correspond to the pattern of the mask, whereby the resulting laser beam has a cross-section corresponding to the pattern when it strikes the surface of the target object.